Study On Variable Geometry Exhaust Manifold Turbocharging System For Vehicle Diesel Engine

The constant-pressure turbocharging system and the pulse turbocharging system are two basic turbocharging systems. The exhaust manifold volume of the constant-pressure turbocharging system is large. The negative pumping work of the constant-pressure turbocharging system is less than that of the pulse turbocharging system during the high speed operation. It is because that the exhaust pressure in exhaust manifold becomes smaller during most of the forced exhaust stage. So the constant-pressure turbocharging system works better during the high speed operation. The pulse turbocharging system has a relatively small exhaust manifold volume, which avoids scavenging interference and gets the pulse energy better utilized. It works better during the low speed or the transient response operation. On the basis of these two fundamental turbocharging systems come four more turbocharging systems, namely the pulse converter (PC), the modular pulse converter (MPC), the mixed pulse converter (MIXPC) and the modular multi-purpose pulse converter (MMPC) turbocharging systems. A key weak point of all these turbocharging systems is that they cannot work well at both the high speed and the low speed operations because that the manifold structure is fixed.. The variable geometry exhaust manifold (VGEM) turbocharging system can realize the switch between two charging modes by the controllable valves. When the controllable valves are closed during the low speed or transient response operation, the VGEM turbocharging system works as a pulse turbocharging system and the pulse energy get better utilized. When the controllable valves turn opened during the high speed operation, the VGEM turbocharging system turns to work as a semi-constant pressure turbocharging system, which reduces the pumping loss.In this paper, the study on the VGEM turbocharging system for vehicle diesel engine has been carried out. Firstly, the experiment of the three pulse turbocharging system is carried out. The variation rules of the BSFC, the smoke, the PMEP and the exhaust pressure wave are analyzed.Then, the simulation of the VGEM turbocharging system has been done by GT-POWER, and six models of the VGEM turbocharging system have been simulated. The simulation results indicate that at the 2200 rpm experiment point, the BSFC is lower when the controllable valve is opened. At the 1300 rpm experiment point, the BSFC is lower when the controllable valve is closed. Finally, simulated experiments have been done on one of the six VGEM turbocharging systems. Two charging modes of VGEM have been simulated by changing the exhaust manifold structure, from the original exhaust manifold, which is a pulse turbocharging system, to the newly designed exhaust manifold, which is a semi-constant pressure turbocharging system. The experimental results indicate that when the controllable valve is closed at the low speed operation, the turbocharging system works as a pulse turbocharging system and more pulse energy get utilized. When the controllable valve turns opened at the high speed operation, the turbocharging system works as a semi-constant pressure turbocharging system, which reduces the pumping loss. The experimental results can be reflected by the simulation results.